Nonvolatile semiconductor memory device

ABSTRACT

A control circuit is configured to, during an erase operation, set a voltage of a first line connected to a selected cell unit to a voltage larger than a voltage of a gate of a first transistor included in the selected cell unit by an amount of a first voltage. The control circuit is configured to, during the erase operation, set a voltage difference between a voltage of a first line connected to an unselected cell unit and a voltage of a gate of a first transistor included in the unselected cell unit to a second voltage, the second voltage differing from the first voltage. In addition, the control circuit is configured to, during the erase operation, apply in the selected cell unit and the unselected cell unit a third voltage to a gate of at least one of dummy memory transistors in a dummy memory string, and apply a fourth voltage to a gate of another one of the dummy memory transistors in the dummy memory string, the fourth voltage being lower than the third voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/263,868, filed Apr. 28, 2014, which is a continuation of U.S.application Ser. No. 13/870,137, filed Apr. 25, 2013, now U.S. Pat. No.8,830,765, which is a continuation of U.S. application Ser. No.13/233,407, filed Sep. 15, 2011, now U.S. Pat. No. 8,446,780, which isbased upon and claims the benefit of priority from the prior JapanesePatent Application No. 2010-211865, filed on Sep. 22, 2010, the entirecontents of each of which are incorporated herein by reference.

FIELD

Embodiments described in the present specification relate to anelectrically data rewritable nonvolatile semiconductor memory device.

BACKGROUND

In recent years, many semiconductor memory devices having memory cellsdisposed three-dimensionally are proposed as a way of increasing adegree of integration of memory. For example, one conventional kind ofsemiconductor memory device having memory cells three-dimensionallydisposed employs a transistor having a cylindrical column-shapedstructure.

There is a risk that, when an erase operation is executed on asemiconductor memory device of the above-described kind, the eraseoperation is not executed accurately due to a leak current flowing intothe memory cells from various kinds of wiring lines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a nonvolatile semiconductor memory deviceaccording to a first embodiment.

FIG. 2 is a circuit diagram of a memory cell array 1 according to thefirst embodiment.

FIG. 3 is a schematic perspective view of the nonvolatile semiconductormemory device according to the first embodiment.

FIG. 4 is a cross-sectional view of the nonvolatile semiconductor memorydevice according to the first embodiment.

FIG. 5 is an enlarged view of FIG. 4.

FIG. 6 is a schematic view showing an erase operation in the nonvolatilesemiconductor memory device according to the first embodiment.

FIG. 7 is a timing chart of during the erase operation in thenonvolatile semiconductor memory device according to the firstembodiment.

FIG. 8 is a circuit diagram of a memory cell array 1 according to asecond embodiment.

FIG. 9A is a schematic view showing an erase operation in a nonvolatilesemiconductor memory device according to the second embodiment.

FIG. 9B is a schematic view showing the erase operation in thenonvolatile semiconductor memory device according to the secondembodiment.

FIG. 10 is a timing chart of during the erase operation in thenonvolatile semiconductor memory device according to the secondembodiment.

FIG. 11 is a circuit diagram of a memory cell array 1 according to athird embodiment.

FIG. 12 is a cross-sectional view of a nonvolatile semiconductor memorydevice according to the third embodiment.

FIG. 13 is a schematic view showing an erase operation in a nonvolatilesemiconductor memory device according to another embodiment.

FIG. 14 is a circuit diagram showing a dummy memory string DMS in anonvolatile semiconductor memory device according to a modified example.

FIG. 15 is a circuit diagram showing a memory string MS in a nonvolatilesemiconductor memory device according to a modified example.

DETAILED DESCRIPTION

A nonvolatile semiconductor memory device according to an embodimentcomprises a cell unit, a first line, and a control circuit. The cellunit includes a plurality of memory transistors. The first line isconnected to one end of the cell unit. The control circuit is configuredto control a voltage applied to the cell unit. The cell unit comprises amemory string, a dummy memory string, and a first transistor. The memorystring has a plurality of electrically rewritable memory transistorsconnected in series. The dummy memory string has one end connected toone end of the memory string, and has a plurality of dummy memorytransistors connected in series. The first transistor is providedbetween the other end of the dummy memory string and the first line. Thememory string comprises a semiconductor layer, a charge storage layer,and a first conductive layer. The semiconductor layer includes acolumnar portion extending in a perpendicular direction to a substrateand functions as a body of the memory transistors. The charge storagelayer surrounds aside surface of the columnar portion and stores acharge. The first conductive layer surrounds a side surface of thecolumnar portion via the charge storage layer and functions as a gate ofthe memory transistors. The dummy memory string comprises thesemiconductor layer, the charge storage layer, and a second conductivelayer. The semiconductor layer functions as a body of the dummy memorytransistors. The second conductive layer surrounds aside surface of thecolumnar portion via the charge storage layer and functions as a gate ofthe dummy memory transistors. The control circuit is configured to,during an erase operation, set a voltage of the first line connected toa selected cell unit to a voltage larger than a voltage of agate of thefirst transistor included in the selected cell unit by an amount of afirst voltage. The control circuit is configured to, during the eraseoperation, set a voltage difference between a voltage of the first lineconnected to an unselected cell unit and a voltage of a gate of thefirst transistor included in the unselected cell unit to a secondvoltage, the second voltage differing from the first voltage. Inaddition, the control circuit is configured to, during the eraseoperation, apply in the selected cell unit and the unselected cell unita third voltage to a gate of at least one of the dummy memorytransistors in the dummy memory string, and apply a fourth voltage to agate of another one of the dummy memory transistors in the dummy memorystring, the fourth voltage being lower than the third voltage.

A nonvolatile semiconductor memory device according to an embodimentcomprises a cell unit, a first line, and a control circuit. The cellunit includes a plurality of memory transistors. The first line isconnected to one end of the cell unit. The control circuit is configuredto control a voltage applied to the cell unit. The cell unit comprises amemory string and a first transistor. The memory string has a pluralityof electrically rewritable memory transistors connected in series. Thefirst transistor is provided between one end of the memory string andthe first line. The memory string comprises a semiconductor layer, acharge storage layer, and a first conductive layer. The semiconductorlayer includes a columnar portion extending in a perpendicular directionto a substrate and functions as a body of the memory transistors. Thecharge storage layer surrounds a side surface of the columnar portionand stores a charge. The first conductive layer surrounds a side surfaceof the columnar portion via the charge storage layer and functions as agate of the memory transistors. The control circuit is configured to,during an erase operation, set a voltage of the first line connected toa selected cell unit to a voltage larger than a voltage of a gate of thefirst transistor included in the selected cell unit by an amount of afirst voltage. The control circuit is configured to, during the eraseoperation, set a voltage difference between a voltage of the first lineconnected to an unselected cell unit and a voltage of a gate of thefirst transistor included in the unselected cell unit to a secondvoltage, the second voltage differing from the first voltage. Inaddition, the control circuit is configured to, during the eraseoperation, execute a first process and a second process. The firstprocess is a process in which, in the selected memory cell unit and theunselected memory cell unit, a third voltage is applied to a gate of atleast one of the memory transistors in the memory string, and a fourthvoltage is applied to a gate of another one of the memory transistors inthe memory string, the fourth voltage being lower than the thirdvoltage. The second process is a process in which the fourth voltage isapplied to the gate of the memory transistors applied with the thirdvoltage in the first process, and the third voltage is applied to thegate of the memory transistors applied with the fourth voltage in thefirst process.

An embodiment of a nonvolatile semiconductor memory device is describedbelow with reference to the drawings.

[First Embodiment]

[Configuration]

First, a configuration of a nonvolatile semiconductor memory deviceaccording to a first embodiment is described with reference to FIGS. 1and 2. As shown in FIG. 1, the nonvolatile semiconductor memory deviceaccording to the first embodiment includes a memory cell array 1 and acontrol circuit 1A.

As shown in FIG. 1, the memory cell array 1 includes a plurality ofmemory blocks MB. Furthermore, each memory block MB includes a pluralityof cell units MU, a bit line BL, and a source line SL. The cell unit MUis selected when an erase operation for erasing data is executed. Asshown in FIG. 3 mentioned later, the cell unit MU is disposed having itslonger direction as a stacking direction. That is, the cell unit MU isarranged three-dimensionally. The bit line BL is connected to a drainside of the cell unit MU. The source line SL is connected to a sourceside of the cell unit MU.

The control circuit 1A controls a voltage applied to the memory cellarray 1 (cell unit MU). As shown in FIG. 1, the control circuit 1Acomprises row decoders 2, 3, a sense amplifier 4, a column decoder 5,and a control signal generating unit (high voltage generating unit) 6.

The row decoders 2, 3 decode a block address signal and so on downloadedto the row decoders 2, 3, and control the memory cell array 1. The senseamplifier 4 reads data from the memory cell array 1. The column decoder5 decodes a column address signal and controls the sense amplifier 4.The control signal generating unit 6 boosts a base voltage to generate ahigh voltage required during write and erase, and furthermore, generatesa control signal to control the row decoders 2, 3, the sense amplifier4, and the column decoder 5.

Next, a circuit configuration of the memory cell array 1 is describedspecifically, with reference to FIG. 2. As shown in FIG. 2, the memorycell array 1 includes a plurality of memory blocks MB<1>, . . . , MB<n>,a plurality of bit lines BL<1>, . . . , BL<n>, and a plurality of sourcelines SL<1>, . . . , SL<n>. Note that when none of the plurality ofmemory blocks MB<1>, . . . , MB<n> is specified, they are collectivelytermed memory blocks MB. When none of the plurality of bit lines BL<1>,. . . , BL<n> is specified, they are collectively termed bit lines BL.When none of the plurality of source lines SL<1>, . . . , SL<n> isspecified, they are collectively termed source lines SL.

Each memory block MB includes a plurality of cell units MU, and isconfigured as a smallest unit of the erase operation. The bit lines BLare commonly provided to the memory blocks MB<1>, . . . , MB<n>. The bitlines BL are commonly connected to drains of a plurality of cell unitsMU in one of the memory blocks MB. The source lines SL are each providedso as to be divided on a memory block MB basis. That is, the sourcelines SL are partitioned on a memory block MB basis, and are providedindependently one each to each one of the memory blocks MB. The sourcelines SL are connected to sources of a plurality of the cell units MU.

In the example shown in FIG. 2, the cell units MU are provided in amatrix along k rows and n columns to each one of the memory blocks MB.Each cell unit MU includes a memory string MS, a dummy memory stringDMS, a drain side select transistor SDTr, and a source side selecttransistor SSTr. The memory string MS is configured by memorytransistors MTr1-MTr4 connected in series. The memory transistorsMTr1-MTr4 are configured such that changing an amount of charge storedin a charge storage layer of the memory transistors MTr1-MTr4 causes athreshold voltage of the memory transistors MTr1-MTr4 to change.Changing the threshold voltage allows data retained in the memorytransistors MTr1-MTr4 to be rewritten.

A source of the dummy memory string DMS is connected to a drain of thememory string MS (drain of the memory transistor MTr4). The dummy memorystring DMS is configured by dummy memory transistors DMTr1-DMTr4connected in series. The dummy memory transistors DMTr1-DMTr4 are notemployed in storage of data, but are employed for controlling a voltageof a body of the memory transistors MTr1-MTr4. Note that a function ofthe dummy memory transistors DMTr1-DMTr4 is described in detail in FIG.6 mentioned later.

A source of the drain side select transistor SDTr is connected to adrain of the dummy memory string DMS (drain of the dummy memorytransistor DMTr4). A drain of the source side select transistor SSTr isconnected to a source of the memory string MS (source of the memorytransistor MTr1).

As shown in FIG. 2, in the plurality of memory blocks MB, gates of thememory transistors MTr1 arranged in a matrix are commonly connected to asingle word line WL1. Similarly, gates of the memory transistorsMTr2-MTr4 are commonly connected to single word lines WL2-WL4,respectively.

As shown in FIG. 2, in the memory block MB<1>, gates of the drain sideselect transistors SDTr arranged in a line in a row direction arecommonly connected to a single drain side select gate line SGD<1,1> (orSGD<1,2>, SGD<1,k>). Similarly, in each of the memory blocks MB<n>,gates of the drain side select transistors SDTr arranged in a line in arow direction are commonly connected to a single drain side select gateline SGD<n,1> (or SGD<n,2>, . . . , SGD<n,k>). Note that when none ofthe drain side select gate lines SGD<1,1>, . . . , SGD<n,k> isspecified, they are collectively termed drain side select gate linesSGD. The drain side select gate lines SGD are each provided extending inthe row direction and having a certain pitch in a column direction.

In addition, drains of the drain side select transistors SDTr arrangedin a line in the column direction are commonly connected to a single bitline BL1 (or BL2, . . . , BLn). The bit lines BL are formed extending inthe column direction straddling the memory blocks MB.

As shown in FIG. 3, in the memory block MB<1>, gates of the source sideselect transistors SSTr arranged in a line in the row direction arecommonly connected to a single source side select gate line SGS<1,1> (orSGS<1,2>, . . . , SGS<1,k>). Similarly, in each of the memory blocksMB<n>, gates of the source side select transistors SSTr arranged in aline in a row direction are commonly connected to a single source sideselect gate line SGS<n,1> (or SGS<n,2>, . . . , SGS<n,k>). Note thatwhen none of the source side select gate lines SGS<1,1>, . . . ,SGS<n,k> is specified, they are collectively termed source side selectgate lines SGS. The source side select gate lines SGS are each providedextending in the row direction and having a certain pitch in the columndirection.

In addition, all of the source side select transistors SSTr in thememory block MB<1> are commonly connected to a single source line SL<1>.Similarly, all of the source side select transistors SSTr in the memoryblock MB<n> are commonly connected to a single source line SL<n>.

Such an above-described circuit configuration of the memory cell array 1is realized by a stacking structure shown in FIGS. 3 and 4. As shown inFIGS. 3 and 4, the nonvolatile semiconductor memory device according tothe first embodiment includes a semiconductor substrate 10, and, stackedsequentially on the semiconductor substrate 10, a source side selecttransistor layer 20, a memory layer 30, a drain side select transistorlayer 40, and a wiring layer 50.

The semiconductor substrate 10 functions as the source line SL. Thesource side select transistor layer 20 functions as the source sideselect transistor SSTr. The memory layer 30 functions as the memorystring MS (memory transistors MTr1-MTr4) and the dummy memory string DMS(dummy memory transistors DMTr1-DMTr4). The drain side select transistorlayer 40 functions as the drain side select transistor SDTr. The wiringlayer 50 functions as the bit line BL, and other various kinds of wiringlines.

The semiconductor substrate 10 includes, on its upper surface, adiffusion layer 11. The diffusion layer 11 functions as the source lineSL. The diffusion layer 11 is divided on a memory block MB basis.

As shown in FIGS. 3 and 4, the source side select transistor layer 20includes a source side conductive layer 21 on the semiconductorsubstrate 10 via an insulating layer. The source side conductive layer21 functions as a gate of the source side select transistor SSTr and asthe source side select gate line SGS. The source side conductive layer21 is formed in stripes extending in the row direction and having acertain pitch in the column direction in each memory block MB. Thesource side conductive layer 21 is configured by polysilicon (poly-Si).

In addition, as shown in FIG. 4, the source side select transistor layer20 includes a source side hole 22. The source side hole 22 is formedpenetrating the source side conductive layer 21. The source side holes22 are formed in a matrix in the row direction and the column direction.

Moreover, as shown in FIG. 4, the source side select transistor layer 20includes a source side gate insulating layer 23 and a source sidecolumnar semiconductor layer 24. The source side columnar semiconductorlayer 24 functions as a body (channel) of the source side selecttransistor SSTr.

The source side gate insulating layer 23 is formed with a certainthickness on a side wall of the source side hole 22. The source sidecolumnar semiconductor layer 24 is formed to be in contact with a sidesurface of the source side gate insulating layer 23 and to fill thesource side hole 22. The source side columnar semiconductor layer 24 isformed in a column shape extending in the stacking direction. The sourceside columnar semiconductor layer 24 is formed on the diffusion layer11. The source side gate insulating layer 23 is configured by siliconoxide (SiO₂). The source side columnar semiconductor layer 24 isconfigured by polysilicon (poly-Si).

Expressing the above-described configuration of the source side selecttransistor layer 20 in other words, the source side conductive layer 21is formed to surround the source side columnar semiconductor layer 24via the source side gate insulating layer 23.

As shown in FIG. 4, the memory layer 30 includes word line conductivelayers 31 a-31 h stacked sequentially via insulating layers on thesource side select transistor layer 20. The word line conductive layers31 a-31 d function as gates of the memory transistors MTr1-MTr4 and asthe word lines WL1-WL4. The word line conductive layers 31 e-31 hfunction as gates of the dummy memory transistors DMTr1-DMTr4 and asdummy word lines DWL1-DWL4.

The word line conductive layers 31 a-31 h are formed along the pluralityof memory blocks MB so as to spread two-dimensionally (in a plate-likeshape) in the row direction and the column direction. The word lineconductive layers 31 a-31 h are configured by polysilicon (poly-Si).

In addition, as shown in FIG. 4, the memory layer 30 includes a memoryhole 32. The memory hole 32 is formed penetrating the word lineconductive layers 31 a-31 h. The memory holes 32 are formed in a matrixin the row direction and the column direction. The memory hole 32 isformed at a position aligning with the source side hole 22.

Moreover, as shown in FIG. 4, the memory layer 30 includes a memory gateinsulating layer 33 and a memory columnar semiconductor layer 34. Thememory columnar semiconductor layer 34 functions as a body (channel) ofthe memory transistors MTr1-MTr4. In addition, the memory columnarsemiconductor layer 34 functions as a body (channel) of the dummy memorytransistors DMTr1-DMTr4.

The memory gate insulating layer 33 is formed with a certain thicknesson a side wall of the memory hole 32. The memory columnar semiconductorlayer 34 is formed to be in contact with a side surface of the memorygate insulating layer 33 and to fill the memory hole 32. The memorycolumnar semiconductor layer 34 is formed in a column shape extending inthe stacking direction. The memory columnar semiconductor layer 34 isformed having its lower surface in contact with an upper surface of thesource side columnar semiconductor layer 24.

A configuration of the memory gate insulating layer 33 is described herein detail with reference to FIG. 5. FIG. 5 is an enlarged view of FIG.4. The memory gate insulating layer 33 includes, from a side of a sidesurface of the memory hole 32 to a side of the memory columnarsemiconductor layer 34, a block insulating layer 33 a, a charge storagelayer 33 b, and a tunnel insulating layer 33 c. The charge storage layer33 b is configured capable of storing a charge.

As shown in FIG. 5, the block insulating layer 33 a is formed with acertain thickness on a side wall of the memory hole 32. The chargestorage layer 33 b is formed with a certain thickness on a side wall ofthe block insulating layer 33 a. The tunnel insulating layer 33 c isformed with a certain thickness on a side wall of the charge storagelayer 33 b. The block insulating layer 33 a and the tunnel insulatinglayer 33 c are configured by silicon oxide (SiO₂). The charge storagelayer 33 b is configured by silicon nitride (SiN). The memory columnarsemiconductor layer 34 is configured by polysilicon (poly-Si).

Expressing the above-described configuration of the memory layer 30 inother words, the word line conductive layers 31 a-31 h are formed tosurround the memory columnar semiconductor layer 34 via the memory gateinsulating layer 33.

As shown in FIGS. 3 and 4, the drain side select transistor layer 40includes a drain side conductive layer 41. The drain side conductivelayer 41 functions as a gate of the drain side select transistor SDTrand as the drain side select gate line SGD.

The drain side conductive layer 41 is stacked via an insulating layer onthe memory layer 30. The drain side conductive layer 41 is formeddirectly above the memory columnar semiconductor layer 34. The drainside conductive layer 41 is formed in stripes extending in the rowdirection and having a certain pitch in the column direction in eachmemory block MB. The drain side conductive layer 41 is configured by,for example, polysilicon (poly-Si).

In addition, as shown in FIG. 4, the drain side select transistor layer40 includes a drain side hole 42. The drain side hole 42 is formedpenetrating the drain side conductive layer 41. The drain side holes 42are formed in a matrix in the row direction and the column direction.The drain side hole 42 is formed at a position aligning with the memoryhole 32.

Moreover, as shown in FIG. 4, the drain side select transistor layer 40includes a drain side gate insulating layer 43 and a drain side columnarsemiconductor layer 44. The drain side columnar semiconductor layer 44functions as a body (channel) of the drain side select transistor SDTr.

The drain side gate insulating layer 43 is formed with a certainthickness on a side wall of the drain side hole 42. The drain sidecolumnar semiconductor layer 44 is formed to be in contact with thedrain side gate insulating layer 43 and to fill the drain side hole 42.The drain side columnar semiconductor layer 44 is formed in a columnshape extending in the stacking direction. The drain side columnarsemiconductor layer 44 is formed having its lower surface in contactwith an upper surface of the memory columnar semiconductor layer 34. Thedrain side gate insulating layer 43 is configured by silicon oxide(SiO₂). The drain side columnar semiconductor layer 44 is configured bypolysilicon (poly-Si).

Expressing the above-described configuration of the drain side selecttransistor layer 40 in other words, the drain side conductive layer 41is formed to surround the drain side columnar semiconductor layer 44 viathe drain side gate insulating layer 43.

As shown in FIGS. 3 and 4, the wiring layer 50 includes a bit layer 51.The bit layer 51 functions as the bit line BL.

The bit layer 51 is formed in contact with an upper surface of the drainside columnar semiconductor layer 44. The bit layer 51 is formedextending in the column direction and having a certain pitch in the rowdirection. The bit layer 51 is configured by a metal such as tungsten.

Next, an erase operation in the nonvolatile semiconductor memory deviceaccording to the first embodiment is described with reference to FIG. 6.In FIG. 6, description proceeds, as an example, assuming that data inthe memory transistors MTr1-MTr4 in memory block MB<1> (selected memoryblock) is selectively erased, while memory block MB<2> (unselectedmemory block) is not selected and erase of data in the memorytransistors MTr1-MTr4 in memory block MB<2> is prohibited. That is, allof the cell units MU (selected cell units) in memory block MB<1> areselected and their data is erased. In addition, all of the cell units MU(unselected cell units) in memory block MB<2> are unselected and theirdata is not erased.

Specifically, as shown in FIG. 6, in memory block MB<1>, a voltage ofthe bit line BL<1> is set to a voltage Vera, and a voltage of the drainside select transistors SDTr is set to a voltage Vera-Δ. In addition, inmemory block MB<1>, a voltage of the source line SL<1> is set to thevoltage Vera, and a voltage of the source side select transistors SSTris set to the voltage Vera-Δ. That is, in memory block MB<1>, thevoltage of the bit line BL<1> is set to a voltage higher than thevoltage of the gates of the drain side select transistors SDTr by anamount of a voltage Δ, and the voltage of the source line SL<1> is setto a voltage higher than the voltage of the gates of the source sideselect transistors SSTr by an amount of the voltage Δ. This causes aGIDL current to be generated in a vicinity of gates of the source sideselect transistors SSTr and drain side select transistors SDTr in memoryblock MB<1>.

In addition, as shown in FIG. 6, in memory block MB<1>, a voltage ofgates of the dummy memory transistors DMTr1, DMTr3 is set to a powersupply voltage Vdd, and a voltage of gates of the dummy memorytransistors DMTr2, DMTr4 is set to a ground voltage (0 V). This causes apotential of the body of the dummy memory transistors DMTr1-DMTr4 to bestructured having a plurality of potential wells (potential barriers).As a result of this potential structure, the dummy memory string DMSallows movement of holes from the drain side select transistor SDTr tothe memory string MS, while at the same time prohibiting movement ofelectrons from the drain side select transistor SDTr to the memorystring MS. In memory block MB<1>, holes generated by the GIDL current inthe vicinity of gates of the drain side select transistors SDTr flowinto the body of the memory transistors MTr1-MTr4, thereby causing avoltage of the body of the memory transistors MTr1-MTr4 to rise.

Subsequently, the voltage of the gates of the memory transistorsMTr1-MTr4 is set to 0 V, that is, is set lower than the voltage of thebody of the memory transistors MTr1-MTr4. This causes a high voltage tobe applied to the charge storage layer of the memory transistorsMTr1-MTr4 in memory block MB<1>, whereby the erase operation on memoryblock MB<1> is executed.

On the other hand, in memory block MB<2>, a voltage of gates of thedrain side select transistors SDTr is set to the voltage Vera. That is,the voltage of the bit line BL<1> is set to the same voltage Vera as thevoltage of the gates of the drain side select transistors SDTr. Inaddition, the source line SL<2> is set to 0 V, and the voltage of thegates of the source side select transistors SSTr is set to a voltageVth. That is, the voltage (Vth) of the gates of the source side selecttransistors SSTr is set higher than the voltage (0 V) of the source lineSL<2> by an amount of the voltage Vth. As a result, in memory blockMB<2>, generation of a GIDL current is prohibited, and the source sideselect transistors SSTr attain a conductive state.

Now, gates of the memory transistors MTr1-MTr4 are shared between memoryblocks MB<1>, MB<2> due to the word lines WL1-WL4. Accordingly, thevoltage of gates of the memory transistors MTr1-MTr4 is set to 0 V notonly in memory block MB<1>, but also in memory block MB<2>.

However, in memory block MB<2>, the voltage of the body of the memorytransistors MTr1-MTr4 is not boosted by the GIDL current. Moreover, evensupposing that some kind of leak current flowed into the body of thecell units MU in memory block MB<2>, the source side select transistorsSSTr in memory block MB<2> are in the conductive state, hence chargeretained in the body of the memory transistors MTr1-MTr4 due to such aleak current is discharged to the source line SL<2>.

Furthermore, gates of the dummy memory transistors DMTr1-DMTr4 areshared between memory blocks MB<1>, MB<2> due to the dummy word linesDWL1-DWL4. Accordingly, even in memory block MB<2>, the dummy memorystring DMS allows movement of holes from the drain side selecttransistor SDTr to the memory string MS, and, moreover, prohibitsmovement of electrons from the drain side select transistor SDTr to thememory string MS.

Therefore, in memory block MB<2>, the body of the memory transistorsMTr1-MTr4 does not have electrons injected therein from the drain sideselect transistors SDTr. That is, leak current flowing from the bit lineBL<1> into memory block MB<2> is suppressed. As a result, in memoryblock MB<2>, voltage rise in the body of the memory transistorsMTr1-MTr4 is suppressed.

As is clear from the above, in memory block MB<2>, the voltage of thebody of the memory transistors MTr1-MTr4 is held at a low voltage.Accordingly, a high voltage is not applied to the charge storage layerof those memory transistors MTr1-MTr4, hence, in the first embodiment,erase error in the unselected memory block MB<2> can be suppressed.

When executing the above-described erase operation, first, at time t11in FIG. 7, the voltage of the dummy word lines DWL2, DWL4 is loweredfrom the power supply voltage Vdd to the ground voltage (0 V).Meanwhile, the voltage of the dummy word lines DWL1, DWL3 is held at thepower supply voltage Vdd. As a result, the potential of the body of thedummy memory transistors DMTr1-DMTr4 configures the above-mentionedplurality of potential wells (potential barriers).

Next, at time t12, the voltage of the bit line BL<1> is raised to thevoltage Vera. The voltage of the source line SL<1> is raised to thevoltage Vera, while the voltage of the source line SL<2> is held at theground voltage (0 V). The voltage of the word lines WL1-WL4 is loweredto the ground voltage (0 V). Additionally, at time t12, the voltage ofthe source side select gate lines SGS<1,1>-SGS<1,k> and the drain sideselect gate lines SGD<1,1>-SGD<1,k> is raised to the voltage Vera-Δ.Further, at time t12, the voltage of the source side select gate linesSGS<2,1>-SGS<2,k> is raised to the voltage Vth. In addition, the voltageof the drain side select gate lines SGD<2,1>-SGD<2,k> is raised to thevoltage Vera.

Subsequently, at time t13, the voltage of the word lines WL1-WL4 israised to the power supply voltage Vdd. Next, at time t14, the voltageof the bit line BL<1>, the source line SL<1>, the source side selectgate lines SGS<1,1>-SGS<1,k>, SGS<2,1>-SGS<2,k>, and the drain sideselect gate lines SGD<1,1>-SGD<1,k>, SGD<2,1>-SGD<2,k> is lowered to theground voltage (0 V). Then, at time t15, the voltage of the dummy wordlines DWL2-DWL4 is raised to the power supply voltage Vdd.

As described above, the control at times t11-t15 allows the firstembodiment to execute the erase operation on memory block MB<1> whilesuppressing erase error on the memory block MB<2>, as shown in FIG. 6.

[Second Embodiment]

Next, a configuration of a nonvolatile semiconductor memory deviceaccording to a second embodiment is described. Note that in the secondembodiment, configurations identical to those in the first embodimentare assigned with identical symbols to those used in the firstembodiment, and a description of those configurations is omitted.

FIG. 8 is a circuit diagram showing a memory cell array 1 in the secondembodiment. As shown in FIG. 8, the memory cell array 1 according to thesecond embodiment does not include the dummy memory string DMS (dummymemory transistors DMTr1-DMTr4). On the other hand, the memory string MSfurther includes memory transistors MTr5-MTr8, in addition to the memorytransistors MTr1-MTr4. The memory transistors MTr5-MTr8 are connected inseries and provided between the memory transistor MTr4 and the drainside select transistor SDTr.

In the plurality of memory blocks MB, gates of the memory transistorsMTr5-MTr8 arranged in a matrix are commonly connected to word linesWL5-WL8, respectively.

Such an above-described circuit configuration of the memory cell array 1is realized by a similar stacking structure to that in FIGS. 3 and 4 ofthe first embodiment. However, in the second embodiment, the word lineconductive layers 31 e-31 h function as the gates of the memorytransistors MTr5-MTr8 and as the word lines WL5-WL8. Moreover, thememory columnar semiconductor layer 34 functions as a body (channel) ofthe memory transistors MTr5-MTr8.

Next, an erase operation in the nonvolatile semiconductor memory deviceaccording to the second embodiment is described with reference to FIGS.9A and 9B. In FIGS. 9A and 9B, description proceeds, as an example,assuming that memory block MB<1> is subject to erase, while memory blockMB<2> is not selected and erase of data in the memory transistorsMTr1-MTr4 in memory block MB<2> is prohibited.

During the erase operation in the second embodiment, the bit line BL<1>,the source lines SL<1>, SL<2>, the source side select transistors SSTr,and the drain side select transistors SDTr are controlled similarly tothe first embodiment. During the erase operation in the secondembodiment, only the memory transistors MTr1-MTr8 are subject toexecution of different control to that of the first embodiment.

First, as shown in FIG. 9A, the voltage of the gates of the memorytransistors MTr1, MTr3, MTr5, MTr7 is set to the power supply voltageVdd, and the voltage of the gates of the memory transistors MTr2, MTr4,MTr6, MTr8 is set to the ground voltage (0 V).

This causes a potential of the body of the memory transistors MTr1-MTr8to be structured having a plurality of potential wells (potentialbarriers). As a result of this potential structure, the memory string MSallows movement of holes from the drain side select transistor SDTr tothe memory string MS. At the same time, the memory string MS prohibitsmovement of electrons from the drain side select transistor SDTr to thememory string MS. Therefore, in memory block MB<1>, holes generated bythe GIDL current flow into the body of the memory transistors MTr1-MTr8,thereby causing a voltage of the body of the memory transistorsMTr1-MTr8 to rise.

In addition, in memory block MB<1>, the gates of the memory transistorsMTr2, MTr4, MTr6, MTr8 are set to the ground voltage (0 V). Accordingly,in memory block MB<1>, a high voltage is applied to the charge storagelayer of the memory transistors MTr2, MTr4, MTr6, MTr8, whereby theerase operation is executed on those memory transistors MTr2, MTr4,MTr6, MTr8.

Meanwhile, also in memory block MB<2>, the memory string MS allowsmovement of holes from the drain side select transistor SDTr to thememory string MS, and, moreover, prohibits movement of electrons fromthe drain side select transistor SDTr to the memory string MS.

Therefore, in memory block MB<2>, the body of the memory transistorsMTr1-MTr8 does not have electrons injected therein from the drain sideselect transistors SDTr. That is, leak current flowing from the bit lineBL<1> into memory block MB<2> is suppressed. As a result, in memoryblock MB<2>, voltage rise in the body of the memory transistorsMTr1-MTr8 is suppressed.

Next, as shown in FIG. 9B, the gates of the memory transistors MTr2,MTr4, MTr6, MTr8 are set to the power supply voltage Vdd, and the gatesof the memory transistors MTr1, MTr3, MTr5, MTr7 are set to the groundvoltage (0 V).

As a result, similarly to FIG. 9A, the memory string MS allows movementof holes from the drain side select transistor SDTr to the memory stringMS. At the same time, the memory string MS prohibits movement ofelectrons from the drain side select transistor SDTr to the memorystring MS. Therefore, in memory block MB<1>, holes generated by the GIDLcurrent flow into the body of the memory transistors MTr1-MTr8, therebycausing a voltage of the body of the memory transistors MTr1-MTr8 torise.

In addition, in memory block MB<1>, the gates of the memory transistorsMTr1, MTr3, MTr5, MTr7 are set to the ground voltage (0 V). Accordingly,in memory block MB<1>, a high voltage is applied to the charge storagelayer of the memory transistors MTr1, MTr3, MTr5, MTr7, whereby theerase operation is executed on those memory transistors MTr1, MTr3,MTr5, MTr7.

Meanwhile, also in memory block MB<2>, the memory string MS allowsmovement of holes from the drain side select transistor SDTr to thememory string MS, and, moreover, prohibits movement of electrons fromthe drain side select transistor SDTr to the memory string MS.

Therefore, in memory block MB<2>, the body of the memory transistorsMTr1-MTr8 does not have electrons injected therein from the drain sideselect transistors SDTr. That is, leak current flowing from the bit lineBL<1> into memory block MB<2> is suppressed. As a result, in memoryblock MB<2>, voltage rise in the body of the memory transistorsMTr1-MTr8 is suppressed.

As is clear from the above, the second embodiment executes the eraseoperation (hereinafter, first erase operation) on the memory transistorsMTr2, MTr4, MTr6, MTr8 in memory block MB<1> as shown in FIG. 9A.Subsequently, the second embodiment executes the erase operation(hereinafter, second erase operation) on the memory transistors MTr1,MTr3, MTr5, MTr7 in memory block MB<1> as shown in FIG. 9B. Moreover,during execution of the first erase operation and the second eraseoperation, the second embodiment suppresses leak current in memory blockMB<2>, thereby suppressing occurrence of erase error in memory blockMB<2>.

When executing the above-described erase operation, first, at time t21in FIG. 10, the voltage of the bit line BL<1> is raised to the voltageVera. The voltage of the source line SL<1> is raised to the voltageVera, while the voltage of the source line SL<2> is held at the groundvoltage (0 V).

Additionally, at time t21, the voltage of the source side select gatelines SGS<1,1>-SGS<1,k> and the drain side select gate linesSGD<1,1>-SGD<1,k> is raised to the voltage Vera-Δ.

Further, at time t21, the voltage of the source side select gate linesSGS<2,1>-SGS<2,k> is raised to the voltage Vth. In addition, the voltageof the drain side select gate lines SGD<2,1>-SGD<2,k> is raised to thevoltage Vera.

Next, at time t22, the voltage of the word lines WL2, WL4, WL6, WL8 islowered from the power supply voltage Vdd to the ground voltage (0 V).Meanwhile, the voltage of the word lines WL1, WL3, WL5, WL7 is held atthe power supply voltage Vdd. As a result, the potential of the body ofthe memory transistors MTr1-MTr8 configures the above-mentionedpotential wells (potential barriers). Then, as shown in FIG. 9A, controlat these times t21, t22 results in the first erase operation on memoryblock MB<1> being executed, while erase error on memory block MB<2> issuppressed.

Then, at time t23, the voltage of the word lines WL2, WL4, WL6, WL8 israised to the power supply voltage Vdd. Next, at time t24, the voltageof the bit line BL<1>, the source lines SL<1>, SL<2>, the source sideselect gate lines SGS<1,1>-SGS<1,k>, SGS<2,1>-SGS<2,k>, and the drainside select gate lines SGD<1,1>-SGD<1,k>, SGD<2,1>-SGD<2,k> is loweredto the ground voltage (0 V).

Next, at time t25, the voltage of the bit line BL<1> is raised to thevoltage Vera. The voltage of the source line SL<1> is raised to thevoltage Vera, while the voltage of the source line SL<2> is held at theground voltage (0 V).

Additionally, at time t25, the voltage of the source side select gatelines SGS<1,1>-SGS<1,k> and the drain side select gate linesSGD<1,1>-SGD<1,k> is raised to the voltage Vera-Δ.

Further, at time t25, the voltage of the source side select gate linesSGS<2,1>-SGS<2,k> is raised to the voltage Vth. In addition, the voltageof the drain side select gate lines SGD<2,1>-SGD<2,k> is raised to thevoltage Vera.

Next, at time t26, the voltage of the word lines WL1, WL3, WL5, WL7 islowered from the power supply voltage Vdd to the ground voltage (0 V).Meanwhile, the voltage of the word lines WL2, WL4, WL6, WL8 is held atthe power supply voltage Vdd. As a result, the potential of the body ofthe memory transistors MTr1-MTr8 configures the above-mentionedpotential wells (potential barriers). Then, as shown in FIG. 9B, controlat these times t25, t26 results in the second erase operation on memoryblock MB<1> being executed, while erase error on memory block MB<2> issuppressed.

Then, at time t27, the voltage of the word lines WL1, WL3, WL5, WL7 israised to the power supply voltage Vdd. Next, at time t28, the voltageof the bit line BL<1>, the source lines SL<1>, SL<2>, the source sideselect gate lines SGS<1,1>-SGS<1,k>, SGS<2,1>-SGS<2,k>, and the drainside select gate lines SGD<1,1>-SGD<1,k>, SGD<2,1>-SGD<2,k> is loweredto the ground voltage (0 V).

As shown in FIG. 10, the first erase operation is executed at timest21-t24, and then the second erase operation is executed at timest25-t28. That is, after completion of the first erase operation,interval times t24-t25 is inserted, and the second erase operation isexecuted. Therefore, the second embodiment is configured such that awrite operation, read operation, or the like, other than the eraseoperation, is executable in the interval times t24-t25. As a result,increase in operation time is suppressed in the second embodiment.

Third Embodiment

Next, a stacking structure of a nonvolatile semiconductor memory deviceaccording to a third embodiment is described. Note that in the thirdembodiment, configurations identical to those in the first and secondembodiments are assigned with identical symbols to those used in thefirst and second embodiments, and a description of those configurationsis omitted.

FIG. 11 is a circuit diagram showing a memory cell array 1 in the thirdembodiment. As shown in FIG. 11, the memory string MS according to thethird embodiment further includes a back gate transistor BTr between thememory transistor MTr4 and the memory transistor MTr5, in addition tothe configuration of the second embodiment. In the plurality of memoryblocks MB, gates of the back gate transistors BTr arranged in a matrixare commonly connected to a back gate line BG.

Such an above-described circuit configuration of the memory cell array 1is realized by a stacking structure shown in FIG. 12. That is, as shownin FIG. 12, the nonvolatile semiconductor memory device according to thethird embodiment includes, stacked sequentially on the semiconductorsubstrate 10, a back gate layer 60, a memory layer 70, a selecttransistor layer 80, and a wiring layer 90. The back gate layer 60functions as the back gate transistor BTr. The memory layer 70 functionsas the memory string MS (memory transistors MTr1-MTr8). The selecttransistor layer 80 functions as the drain side select transistor SDTrand the source side select transistor SSTr. The wiring layer 90functions as the source line SL and the bit line BL.

As shown in FIG. 12, the back gate layer 60 includes aback gateconductive layer 61. The back gate conductive layer 61 is formed so asto spread two-dimensionally in the row direction and the columndirection parallel to the substrate 10. The back gate layer 60 isconfigured by polysilicon (poly-Si).

As shown in FIG. 12, the back gate conductive layer 61 includes a backgate hole 62. The back gate hole 62 is formed so as to dig out the backgate conductive layer 61. The back gate hole 62 is formed in asubstantially rectangular shape having the column direction as a longerdirection as viewed from an upper surface. The back gate holes 62 areformed in a matrix in the row direction and the column direction.

As shown in FIG. 12, the memory layer 70 is formed in a layer above theback gate layer 60. The memory layer 70 includes word line conductivelayers 71 a-71 d. The word line conductive layer 71 a functions as theword line WL4 and as the gate of the memory transistor MTr4. Inaddition, the word line conductive layer 71 a functions as the word lineWL5 and as the gate of the memory transistor MTr5. The word lineconductive layer 71 b functions as the word line WL3 and as the gate ofthe memory transistor MTr3. In addition, the word line conductive layer71 b functions as the word line WL6 and as the gate of the memorytransistor MTr6. The word line conductive layer 71 c functions as theword line WL2 and as the gate of the memory transistor MTr2. Inaddition, the word line conductive layer 71 c functions as the word lineWL7 and as the gate of the memory transistor MTr7. The word lineconductive layer 71 d functions as the word line WL1 and as the gate ofthe memory transistor MTr1. In addition, the word line conductive layer71 d functions as the word line WL8 and as the gate of the memorytransistor MTr8.

The word line conductive layers 71 a-71 d are stacked sandwichinginsulating layers. The word line conductive layers 71 a-71 d are formedextending in the row direction as a longer direction and having acertain pitch in the column direction. The word line conductive layers71 a-71 d are configured by polysilicon (poly-Si).

As shown in FIG. 12, the memory layer 70 includes a memory hole 72. Thememory hole 72 is formed penetrating the word line conductive layers 71a-71 d and the insulating layers. The memory hole 72 is formed aligningwith a vicinity of an end portion of the back gate hole 62 in the columndirection.

Moreover, as shown in FIG. 12, the back gate layer 60 and the memorylayer 70 include a memory gate insulating layer 73 and a memorysemiconductor layer 74. The memory semiconductor layer 74 functions as abody of the memory transistors MTr1-MTr8 (memory string MS). The memorygate insulating layer 73 includes a charge storage layer for storing acharge, similarly to the above-described embodiments.

The memory semiconductor layer 74 is formed so as to fill the back gatehole 62 and the memory hole 72. The memory semiconductor layer 74 isformed in a U shape as viewed from the row direction. The memorysemiconductor layer 74 includes a pair of columnar portions 74 aextending in the perpendicular direction to the substrate 10, and ajoining portion 74 b configured to join lower ends of the pair ofcolumnar portions 74 a. The memory semiconductor layer 74 is configuredby polysilicon (poly-Si).

Expressing the above-described configuration of the back gate layer 60in other words, the back gate conductive layer 61 is formed to surroundthe joining portion 74 b via the memory gate insulating layer 73. Inaddition, expressing the above-described configuration of the memorylayer 70 in other words, the word line conductive layers 71 a-71 d areformed to surround the columnar portions 74 a via the memory gateinsulating layer 73.

As shown in FIG. 12, the select transistor layer 80 includes a sourceside conductive layer 81 a and a drain side conductive layer 81 b. Thesource side conductive layer 81 a functions as the source side selectgate line SGS and as the gate of the source side select transistor SSTr.The drain side conductive layer 81 b functions as the drain side selectgate line SGD and as the gate of the drain side select transistor SDTr.

The source side conductive layer 81 a is formed in a layer above one ofthe columnar portions 74 a configuring the memory semiconductor layer74, and the drain side conductive layer 81 b which is in the same layeras the source side conductive layer 81 a is formed in a layer above theother of the columnar portions 74 a configuring the memory semiconductorlayer 74. The source side conductive layer 81 a and the drain sideconductive layer 81 b are formed in stripes extending in the rowdirection and having a certain pitch in the column direction. The sourceside conductive layer 81 a and the drain side conductive layer 81 b areconfigured by polysilicon (poly-Si).

As shown in FIG. 12, the select transistor layer 80 includes a sourceside hole 82 a and a drain side hole 82 b. The source side hole 82 a isformed penetrating the source side conductive layer 81 a. The drain sidehole 82 b is formed penetrating the drain side conductive layer 81 b.The source side hole 82 a and the drain side hole 82 b are each formedat a position aligning with the memory hole 72.

As shown in FIG. 12, the select transistor layer 80 includes a sourceside gate insulating layer 83 a, a source side columnar semiconductorlayer 84 a, a drain side gate insulating layer 83 b, and a drain sidecolumnar semiconductor layer 84 b. The source side columnarsemiconductor layer 84 a functions as a body of the source side selecttransistor SSTr. The drain side columnar semiconductor layer 84 bfunctions as a body of the drain side select transistor SDTr.

The source side gate insulating layer 83 a is formed with a certainthickness on a side surface of the source side hole 82 a. The sourceside columnar semiconductor layer 84 a is formed in a column shape to bein contact with a side surface of the source side gate insulating layer83 a and an upper surface of one of the pair of columnar portions 74 aand to extend in the perpendicular direction to the substrate 10. Thesource side columnar semiconductor layer 84 a is configured bypolysilicon (poly-Si).

The drain side gate insulating layer 83 b is formed with a certainthickness on a side surface of the drain side hole 82 b. The drain sidecolumnar semiconductor layer 84 b is formed in a column shape to be incontact with a side surface of the drain side gate insulating layer 83 band an upper surface of the other of the pair of columnar portions 74 aand to extend in the perpendicular direction to the substrate 10. Thedrain side columnar semiconductor layer 84 b is configured bypolysilicon (poly-Si).

The wiring layer 90 includes a source layer 91, a plug layer 92, and abit layer 93. The source layer 91 functions as the source line SL. Thebit layer 93 functions as the bit line BL.

The source layer 91 is formed to be in contact with an upper surface ofthe source side columnar semiconductor layer 84 a and to extend in therow direction. The bit layer 93 is formed to be in contact with an uppersurface of the drain side columnar semiconductor layer 84 b via the pluglayer 92 and to extend in the column direction. The source layer 91, theplug layer 92, and the bit layer 93 are configured by a metal such astungsten. This allows the source line SL to be made more low resistancethan in the first and second embodiments.

[Other Embodiments]

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the inventions. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the inventions. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the inventions.

For example, the source lines SL<1>, . . . , SL<n> according to thefirst through third embodiments are divided on a memory block MB<1>, . .. , MB<n> basis. However, as shown in FIG. 13, a source line SL may becommonly provided to the memory blocks MB<1>, . . . , MB<n>. In thiscase, during the erase operation, the source line SL is applied with thevoltage Vera, and the gates of the source side select transistors SSTrincluded in the unselected memory block MB<2> are applied with thevoltage Vera.

In addition, as a modified example of the first embodiment, the dummymemory string DMS may include m dummy memory transistors DMTr1-DMTrm, asshown in FIG. 14. In this case, for example, gates of the 3i-th dummymemory transistors DMTr3, DMTr6, . . . may be set to the power supplyvoltage Vdd, and gates of the other dummy memory transistors DMTr1,DMTr2, DMTr4, DMTr5, DMTr7 may be applied with the ground voltage (0 V).That is, the modified example of the first embodiment may be configuredsuch that, during the erase operation, in selected cell units MU andunselected cell units MU, the gate of at least one dummy memorytransistor DMTr in the dummy memory string DMS is applied with the powersupply voltage Vdd, and the gates of another dummy memory transistorsDMTr in the dummy memory string DMS are applied with the ground voltage(0 V) which is lower than the power supply voltage Vdd.

Moreover, as a modified example of the second embodiment, the memorystring MS may include m memory transistors MTr1-MTrm, as shown in FIG.15. In this case, for example, gates of the 3i-th memory transistorsMTr3, MTr6, . . . may be set to the power supply voltage Vdd, and gatesof the other memory transistors MTr1, MTr2, MTr4, MTr5, MTr7 may beapplied with the ground voltage (0 V). That is, the modified example ofthe second embodiment may be configured such that, during the eraseoperation, in selected cell units MU and unselected cell units MU, thegate of at least one memory transistor MTr in the memory string MS isapplied with the power supply voltage Vdd, and the gates of anothermemory transistors MTr in the memory string MS are applied with theground voltage (0 V) which is lower than the power supply voltage Vdd.

What is claimed is:
 1. A nonvolatile semiconductor memory devicecomprising: a first memory string including a first selectiontransistor, a first dummy cell, a second dummy cell, a first memorycell, a second memory cell, and a second selection transistor, thesecond selection transistor being disposed above a semiconductorsubstrate, the second memory cell being disposed above the secondselection transistor, the first memory cell being disposed above thesecond memory cell, the first selection transistor being disposed abovethe first memory cell, the first dummy cell and the second dummy cellbeing disposed between the first selection transistor and the firstmemory cell; and a controller configured to perform an erase operationon a condition where a first voltage is applied to a gate of the firstdummy cell, a second voltage is applied to a gate of the second dummycell, and the second voltage is different from the first voltage.
 2. Thedevice according to claim 1, further comprising: a bit line electricallyconnected to one terminal of the first selection transistor; and asource line electrically connected to one terminal of the secondselection transistor.
 3. The device according to claim 2, wherein athird voltage is applied to both the bit line and the source line. 4.The device according to claim 2, wherein the source line is disposedbelow the second selection transistor.
 5. The device according to claim1, wherein a fourth voltage is applied to a gate of the first selectiontransistor, a fifth voltage is applied to a gate of the second selectiontransistor, and the fourth voltage is different from the fifth voltage.6. The device according to claim 5, wherein the fourth voltage is higherthan the fifth voltage.
 7. The device according to claim 5, wherein thefourth voltage is lower than the fifth voltage.